During the operation of a boiler, many of the steam and water tubes expand and contract in response to the thermal effects caused by expansion and contraction. Therefore, the seals, such as those between dead air spaces and the boiler, have been difficult to maintain. Since steel is the principal material used for the construction of boilers, its inelasticity prevents a durable seal from being maintained because in stead of flexing to expand and contract, the material instead is prone to fracture. When cracks or other leaks exist in the boiler, flue-gas that may carry fly-ash, can enter through these leaks and settle in the dead air space or even travel into the boilerhouse. Leakages have an adverse effect on the efficiency of the operation of the boiler and it is therefore desirable to reduce if not eliminate the leakages which occur due to thermal expansion and contraction. Leakages cause excess air to be introduced within the boiler and can increase slagging, cause loss on ignition, increase the need for superheat or reheat attempt or spraying, and increase the corrosion within the boiler. Cracks and leaks have been responsible for upper-furnace slag problems due to excessive air in leakage through cracks and leaks in the penthouse floor. Repairs are frequently needed of the penthouse to remedy these cracks and leaks.
Historically, cracks and leaks have been repaired through welding the steel to contain the leak or crack. However, the weld itself is also subject to thermal expansion and therefore, does not maintain its integrity and when the boiler heats and cools, eventually more cracks and leaks develop.
One such product that has been useful in repairing these leaks is a product distributed under the trademark ISOMEMBRANE®. This product is available from High Temperature Technologies, Inc., a North Carolina corporation, and has been used in sealing cracks and leaks without losing its seal integrity due to thermal expansion and contraction. ISOMEMBRANE® is a flexible high temperature resistant seal. ISOMEMBRANE® has a sandwich construction consisting of layers of high density fibers (ISOBLANKET-E), high temperature adhesive (ISOBOND-E) and a sealing castable (ISOCOAT-E) to finish the surface. It is capable of sealing leaks and cracks in boilers which have an environment that does not allow welds or other sealing means to keep their integrity due to thermal expansion and contraction caused by the heat associated with a boiler.
By way of example, ISOMEMBRANE® has been credited with reducing slagging and improving the operational condition of a boiler in Alabama which resulted in saving the boiler operations nearly $1.7 million dollars annually. However, ISOMEMBRANE® uses a refractory ceramic fibre (RCF) which has been known to cause irritation of the skin, eyes and upper respiratory tract, and can be inhaled and deposited in the lungs if the RCF is fine enough. It has also been alleged that RCFs can produce lung fibrosis, lung cancer, and also mesothelioma following long-term inhalation.
Therefore, it is desirable to have a boiler sealer which has the advantages of ISOMEMBRANE without having RCFs in its construction or composition.